The present invention generally relates to sound signal analyzers. More specifically, the present invention relates to a "front end" sound signal analyzer for detecting and separating individual voices in a complex musical composition.
The term "complex musical composition" as used in the present disclosure should be understood to mean a multi-voiced musical composition, i.e. musical sounds simultaneously played by more than one instrument. The "voices" or sounds of the instruments may be generated by a natural or conventional instrument, including the human voice.
Devices for recognizing aspects of sound waves, for example the fundamental frequency component of a complex sound wave, are disclosed in the prior art. These prior art devices are generally limited to the analysis of a single instrument or vocalist. To the Applicant's knowledge no prior art device discloses means to detect and separate the sounds of an individual instrument from the sounds of a plurality of instruments simultaneously played.
U.S. Pat. No. 4,457,203 to Schoenberg et al. discloses a sound signal automatic detection system which detects and displays the fundamental frequency of notes played on a single instrument. The fundamental frequency is determined by an alternate positive peak voltage and negative peak voltage detector circuit which analyzes the first major positive going peak voltage and the first major negative going peak voltage exceeding threshold voltage values. U.S. Pat. No. 4,377,961 to Bode discloses a fundamental frequency extractor including separate extractors of successively wider frequency bands and having frequency intervals equal to or less than an octave. A method and apparatus for classifying audio signals is disclosed in U.S. Pat. No. 4,542,525 to Hopf which converts the null transitions of an audio frequency signal into two binary pulse sequences which are compared to predetermined pulse lengths and separate pause detection operations logic circuits. U.S. Pat. No. 3,926,088 to Davis et al. discloses an electro-mechanical device to translate movements of the sound producing means of a musical instrument into musical data. A "frequency follower" is shown in U.S. Pat. No. 4,313,361 to Deutsch.
A tone generating device which extracts pitches from input waveform signals and defines the frequency of the generated tone by comparing the extracted pitch to a range of predetermined musical interval difference is shown in U.S. Pat. No. 4,895,060 to Matsumoto. U.S. Pat. No. 4,399,731 to Aoki discloses a music composition device which randomly extracts stored pitch data in accordance with predetermined music conditions. U.S. Pat. No. 4,909,126 to Skinn et al. discloses a mechanical tuning system for a musical instrument.
The foregoing prior art sound signal analyzers do not meet the terms of the present invention which provides novel means to detect, separate and record the sounds of individual instruments in a "complex musical composition." Thus, by utilizing the present invention the viola parts, for example, in a complex musical composition played by a string quartet may be extracted and recorded as musical data.
Musical instruments including the human voice produce fundamental frequencies and overtones (harmonics) of fundamental frequencies. The same note played by different instruments sounds differently because of the overtone structure or timbre of the sound. Overtones add fullness to a musical sound and timbre is one characteristic that can identify the instrument producing the sound.
A sound wave may be represented by a complex wave composed of the fundamental and harmonics or overtones in the proper amplitude and phase relations. The sound wave can therefore be expressed mathematically. Graphically, the structure of a sound wave produced by a musical instrument can be represented by a spectrum graph or frequency spectrum. A frequency spectrum is a representation of the relative amplitudes of the fundamental and harmonics (overtones) as a function of frequency. Frequency spectrums can be used to depict the timbre of the sounds produced by a musical instrument and therefore can be utilized to distinguish different instruments in a complex musical composition.
A frequency spectrum is an instantaneous-acoustical spectrum generally measured during a steady-state period of a musical sound. Musical sounds from different instruments also have characteristic transient properties. The transient properties define a waveform envelope including growth, steady-state and decay characteristics. Reference is made to the excellent work Musical Engineering by Harry F. Olson (McGraw Hill, 1952) which details the formulation of frequency spectrums and is incorporated herein by reference.
It should also be readily understood by those skilled in the art that musical compositions are written within the framework of specific musical keys. Thus, notes unique to the key in which a musical composition is written have a much higher probability of being sounded than notes not associated with that key. As a result, the key in which a musical composition is written car be utilized to further distinguish the several instruments in a complex musical composition.